Limelette P, Hébert S, Hardy V, Frésard R, Simon Ch, Maignan A
Laboratoire LEMA, UMR 6157 CNRS-CEA, Université F. Rabelais, UFR Sciences, Parc de Grandmont, 37200 Tours, France.
Phys Rev Lett. 2006 Jul 28;97(4):046601. doi: 10.1103/PhysRevLett.97.046601. Epub 2006 Jul 25.
We investigate both thermoelectric and thermodynamic properties of the misfit cobalt oxide [Bi1.7Co0.3Ca2O4]RS0.6CoO2. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S0 approximately 60 microV K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximately 50 mJ (mol K2)-1 attesting to strong correlations. Thereby, the comparison between cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit cobalt oxides results from the addition of a spin entropy contribution to an enlarged electronic one.
